This proposal investigates the use of induced pluripotent stem cell (iPSC)-derived endothelial cells (ECs) as surrogates for native ECs to improve our understanding and to better treat a life-threatening vascular disorder, pulmonary hypertension (PAH). To this end we have assembled a multidisciplinary team with expertise in clinical manifestations and pathobiology of PAH, iPSC generation and differentiation, genetics and genomics, bioinformatics and gene therapy and high throughput phosphoflow and microfluidic technologies. Our proposal reflects a unique opportunity to assess three lines of ECs derived from the same patient. This streamlines our ability to test the efficacy of iPSC-ECs as surrogates for native ECs, and to establish the significance of specific genetic alterations. We have a unique opportunity to compare gene variants, epigenetic and gene expression profiles in fibroblast derived iPSC-ECs to those in pulmonary arterial (PA)EC derived iPSC-ECs from the same PAH patients or controls. This should address in an unprecedented manner, how a genetic vulnerability leads to manifest disease. Moreover, we are well placed to investigate the application of gene and pharmaceutical therapy to reverse PAH pathology in iPSC-ECs. Because studies completed to date in the Wu laboratory have established facility with the production of iPSC-ECs, we are positioned to begin with Phase II of this Proposal. To this end, we propose three Specific Aims in Phase II and three in Phase III. Phase II, Aim 1 applies Hi-Seq, Methyl-Seq and RNA-Seq to obtain information on rare gene variants, epigenetic changes and gene expression in PAH and control fibroblast- iPSC-ECs, PAEC-iPSC-ECs and PAECs. Phase II, Aim 2 correlates this genomic information with function, by extensive analysis of the phenotype of these cells using angiogenesis assays and phosphoflow analyses and by assessing homogeneity using a single cell microfluidic approach. Phase II, Aim 3 initiates a partnership with Progenitor Cell Therapy to transfer the technology of producing iPSC-ECs so that it can be ramped up in the future to benefit large populations of patients. In Phase III, Aim 1 utilizes cutting edge gene therapy approaches, such as minicircles and ribosomal DNA vectors, to correct a gene variant in an iPSC-EC. Phase III, Aim 2 investigates how this reverts the PAH-related phenotype of the cell. Phase III, Aim 3 compares the efficacy of fibroblast and PAEC-iPSC-ECs vs. native PAECs to respond to pharmaceuticals to revert the disease phenotype. In summary, our studies should serve as a model to better understand how iPSC-ECs can be used to uncover and treat genetic predisposition to vascular dysfunction in a wide variety of cardiovascular diseases.